DerbyDad03 wrote:

frost line - The limit of penetration of soil by frost.

Doesn't that mean, by definition, that the well house isn't *really*
below the frost line?

Perhaps the published frost line, either now or when the well house
was installed, is/was incorrect.

I think the problem is that the well house isn't undisturbed soil. About 75% of
the metal well house is exposed above grade, including an uninsulated manhole
cover. The floor of the house is below the frost line where the booster pump and
pipes are below.